Ready, set, crawlHow to play: Use cushions, sheets, blankets, and doormats to make a variety of tunnels and bumps for your baby to crawl under and over.

Why babies love it: When an ordinary room becomes a veritable playground, the opportunity for fun seems endless. (And trust us: The photo ops will be worth every minute of cleanup time.)

What it teaches: Motivation. Once your baby gets into the maze of tunnels and hills, she'll be so curious about how she got in -- and how to find her way out -- that she'll draw on many of her newly learned physical and cognitive skills to help. "This kind of integration of different skills shows a child that she can rely on herself to find the answers," says Claire Lerner, director of parenting resources for Zero to Three, a nonprofit organization.

When to start playing: 8 months and up, when she has the motor skills to crawl and pull herself up.

Beyond peekabooHow to play: Hold a burp cloth in front of your face and ask "Where's Mommy?" but don't pull the cloth away yourself. Wait for your baby to do it. When he reaches for it and sees you, say "Here's Mommy!"

Why babies love it: "Finding" you -- someone your baby knows and loves -- is a sweet surprise every time (and we mean every time: This is not a game he'll let you play just once!). The funny face you'll probably make when your baby pulls away the cloth ups the thrill factor, and he'll imitate you.]

What it teaches: Manipulation skills. (Don't worry: not in a conniving, you'd-better-watch-out-later-on kind of way.) This game helps him understand that when he behaves a certain way, people will do specific things, like pick him up if he cries or smile back if he coos. He learns that by removing the cloth, he can control what he sees.

When to start playing: 6 to 9 months, when your baby has the motor skills to reach for the cloth.

Meghan Rabbitt also writes for Prevention, Shape, and Family Circle.

In the nursery

Hey baby, hey baby, heyHow to play: Stand on one side of the crib and call your baby's name until she turns her head toward you. Then move to the other side and call her name until she faces you again.

Why babies love it: Your voice is still the sweetest, most satisfying sound in your little one's world -- and hearing you call her name will delight her.

What it teaches: Concentration skills. Since your baby has to process where your voice is coming from, her brain is learning to integrate hearing with seeing, which will aid her in focusing later on. "This helps babies learn how to localize something in their environment by listening closely," says David Perlmutter, M.D., author of Raise a Smarter Child by Kindergarten.

When to start playing: Birth to 6 months, when your baby's vision is still a little fuzzy and she won't use her eyes to follow you without an auditory cue. (By 6 months, sight becomes a baby's dominant sense.)

You oughta be in picturesHow to play: Snap some head shots of the important people in your baby's life (you, your husband, older sibs, the babysitter) and get your faraway relatives to e-mail some, too. Print the pictures, mount them on colorful construction paper, and tape together. As your baby looks at each image, name the person in the shot.

Why babies love it: Since they learn early on how to recognize their mother's face, babies find anything that looks similar to be a treat.

What it teaches: Discrimination skills. "Throughout a child's first few years, helping him differentiate is one of the best primers for learning -- it's what helps to build the most sophisticated brain," says Dr. Perlmutter. This game enhances a baby's ability to learn subtle differences, rather than just recognize his parents. Since Dad may look an awful lot like Uncle Bob, a baby has to pick out subtleties -- like brown hair versus blond -- to distinguish between similar faces.

When to start playing: Around 6 months, when a baby's vision has developed and he has the cognitive ability to see smaller differences in pictures.

Light my mobileHow to play: Dim the lights and shine a flashlight on the mobile above your baby's head to cast shadows on the wall beside it. Next, hold the light closer and then farther away so the size of the shadows changes.

Why babies love it: Transforming what used to be simple animals into an ever-evolving zoo is exciting and awe-inspiring.

What it teaches: Memory skills. By temporarily altering a familiar standby in your baby's nursery, you're challenging him to remember what his mobile used to look like. When the flashlight's off and the hanging bears look like themselves again, your baby will recognize there's been a change, which ultimately sharpens his brain synapses, says Dr. Perlmutter.

When to start playing: Birth to 6 months, when your baby's still transfixed by his mobile.

In the bath

Finish that tuneHow to play: When your baby's splashing around, start singing her favorite song (it doesn't matter if you sound like someone from week one of the American Idol auditions). Right before a word or phrase that's repeated a lot, stop singing and wait for her to fill in the rest -- even if she just babbles and coos.

Why babies love it: Just like us, little ones like to have their turn -- and your excited reaction when she chimes in is all the encouragement she needs to feel a sense of pride.

What it teaches: Communication skills. "Even if your child can't verbally fill in the word, her brain will be making the connection, forcing her to draw on her memory to try to find the word," says Dr. Perlmutter. By giving your child a chance to respond, you're building the foundation of conversation.

When to start playing: 8 to 12 months, when a baby's sense of how to communicate is growing at warp speed and she's on the verge of uttering her first word.

Baby scoopsHow to play: Give your baby a few plastic measuring cups or bowls and let him scoop and pour water from each. Next, you scoop and pour over his head (not his face, though) and body so he can feel the difference in how much water comes out of the different containers.

Why babies love it: This gets them going in the same way that plucking out every last tissue from the box does. "When a child realizes that something he does can make something else happen, it's a powerful feeling -- especially considering that he's been completely dependent on you up to now," says Lerner.

What it teaches: Visual-spatial skills. It might seem like your baby's just having a good time pouring water on everything from his tugboat to the bath mat outside the tub, but scooping and pouring water from different-size containers helps him understand the concepts of "bigger" and "smaller" and enhances his understanding of size and shape.

When to start playing: 6 to 9 months, when he has the hand-eye coordination to scoop the water and dump it out and can sit up in the bathtub while doing it. (Just remember that no matter how well your baby can sit up on his own, never leave him alone in the bath.)

On a walk

[BOLD {Touchy-feely fun}]How to play: Instead of going for a power walk, pull over every time you see something with a new texture. Let your baby feel a rough brick wall, a bumpy tree trunk, a soft flower, or a pointy evergreen bush. And be sure to describe each in detail as your baby explores.

Why babies love it: Discovering new textures is exciting for her developing sense of touch, and since she's familiar with these objects -- but has mostly just blown by them in the stroller or car -- actually feeling them makes them come alive in a new way.

What it teaches: A sense of exploration. Your baby has thrived on lots of touch from you, through cuddling, hugs, and all her soft clothes and blankets. When she touches new objects, it helps her sense of discovery grow. There's good news for you here, too: Since this game helps a baby get comfortable with the feel of different objects in her environment, she may be less likely to protest when, say, you want her to sit in the sand or grass later on.

When to start playing: 6 months and up, when she's got the strength to sit up in her stroller and reach for objects.

The need for speedHow to play: For one block, pick up the speed so the stroller zooms along the sidewalk; then slow down to your normal -- or an even slower-than-usual -- pace. Continue altering the speed from fast to slow (until you need a break!).

Why babies love it: "Just as a lot of adults like roller coasters, most babies burst with anticipation and excitement after moving unusually fast," says Lerner. It's the same kind of thrilling sensation your baby has when he's tossed in the air and caught by the reckless uncle you'd like to strangle (but won't because your baby's laughing too hard).

What it teaches: The concept of speed. For the first few months of your baby's life, his day-to-day activities move at a fairly slow pace. When you introduce this new movement, it helps him distinguish between fast and slow.

When to start playing: 6 months and up, when your baby's sense of motion is more refined and he has the trunk and neck strength to sit up and enjoy the ride.